> posix_user:
> 
> * stdlib: '~/.local/lib64/python3.9'
> * platstdlib: '~/.local/lib64/python3.9'
> * platlib: '~/.local/lib64/python3.9/site-packages'

Honestly, I have no idea how posix_user is used.

~/.local/lib64/ directory doesn't exist on my work machine, whereas I'm installed various Python modules and applications.

In practice, ~/.local/lib/ is used on Fedora, even if posix_user scheme uses ~/.local/lib64/. Examples:

* pure Python: ~/.local/lib/python3.7/site-packages/pip/__main__.py
* C extension: ~/.local/lib/python3.7/site-packages/typed_ast/_ast3.cpython-37m-x86_64-linux-gnu.so

So changing posix_user should have no impact on end users.


I also tested a legacy "python3 setup.py install" to install a C extension, it also lands into ~/.local/lib:

~/.local/lib/python3.7/site-packages/test_cext-0.0.0-py3.7-linux-x86_64.egg/test_cext.cpython-37m-x86_64-linux-gnu.so

The setup.py uses setuptools.


Miro:
> Also note that the extension modules have archful suffix, so they will not collide in $HOME, unless they are installed as name.so.

Yeah, it seems like pip install adopted Debian multiarch naming: "x86_64-linux-gnu" triplet in "_ast3.cpython-37m-x86_64-linux-gnu.so" filename.